1. Field of the Invention
The invention relates to a sealed bearing rotary rock bit and more particularly to a ball plug assembly therefor having a resilient ring element for eliminating weld material from entering the sealed lubricant volume during assembly of the bit.
2. Description of the Prior Art
It is well known, and a common practice, to retain the rotary cutter of a rotary rock bit on the journal axle thereof through an annular array of roller bearings or balls disposed between opposed, facing races of the journal and bearing cavity or internal bore of the cutter. Typically, during assembly, the conical cutter is placed over and mounted on the journal axle, and a number of properly sized steel balls are inserted into the space between the opposed annular races through a ball passage communicating with such annular space from the back of the bit leg. After the balls have been inserted to fill the annular space, the conical cutter is axially retained on the journal by the interference of the balls preventing axial displacement of the cutter. To complete the assembly of the cutter on each leg of the bit, the ball passage is itself blocked by an elongated plug member which is inserted into the ball passage, to prevent the balls from escaping.
The plug is generally a cylindrical rod, contoured at the interior end to form a portion of the journal raceway and sized at the opposite end to slidingly fit within the passage in a manner that permits relatively easy rotation of the plug so that, once inserted, the plug can be turned to place the contoured end in proper alignment in the ball raceway as indicated by an exteriorly observed contoured face on the opposite end. Intermediate the two ends, the rod defines a reduced diameter, or necked-down section, providing an annular space that permits the ball passage to subsequently function as a portion of the lubricant distributing system of the rotary rock bit.
To retain the ball plug itself, the enlarged exposed end is welded into the proper final position. It has been found that during the welding operation, contaminating weld material such as slag, can, on occasion, escape between the ball passage and the plug (remembering that the fit must be such that the plug is readily rotated within the passage) into the volume of the necked-down portion, and become entrained in the lubricant, as it is subsequently injected into the lubricant system and bearing cavity of the bit. Such contaminated lubricant, when distributed to the highly loaded bearings within the cutter and journal during operation, causes rapid degradation of the bearing surfaces which contributes to premature failure of the bearings.